In every game of zombies played most people die because some one does something wrong and it is something every one does from time to time, so what might you be doing wrong.
1. Gun and ammo management.
Some times you or someone you know will have an under powered gun, a bad gun at a bad time or not have any ammo when it is need. managing what guns you have sounds like something every one does but really it is pushed off to the side when it matters. When you have a MPL and it is wave 14 you are going to see a game over screen unless you switch to a gun that takes less then a clip to kill a zombie. you all know controlling your ammo supply is not the essayist thing to do but is needed if you want to make it pass wave 20, having the Afterburner in late waves is not the best thing to do because it burns though ammo and when you burn though ammo it becomes harder to maintain your camping spot because you can not kill zombies when you do not have ammo. People can keep a good supply of ammo by having an idea when the last max ammo was and switching your guns based on max ammo's.
2. Picking a bad camp spot.
You want a camping spot close to the random box but only if it has an emergency exit, up to two entry ways a max of two windows and make sure the entry points are narrow. Some players just stay with the random box no matter what their situation is. They could have Famas with a clip and a half at wave 18 with the box moving to different area of the map and they will follow it being chased by a mob. Remember with more players you can hold down a bigger area but that does not mean it is a good idea to stay in a big area because big areas have more entry points allowing zombies to come in and attack you from multiple sides.
3. Spending points
Just because someone has 2200 points does not mean they should spend all of it on the box but the fact that they are only 300 points away from juggernaut does not stop them from making the wrong choice. When you are close to a upgrade or a perk you should wait until you get the points to get what you need. When you are playing with other people it is a good idea to buy the doors in a equal manner so every one has a similar amount of points. Making sure every one has similar amount of points is important because some one could buy all the doors to the power might not have enough points to buy a gun making you cover your window and their window giving you more points and keeping their points low. There is a part of every zombie game that you get into a good camp area with two or more players watching over the main entry way and getting a lot of points with one player on a window get enough points to buy the random box two times to prevent one player getting little amount of points groups should rotate were they are so every one gets the window allowing every one to get points for upgrading or buying perks.
4. Stay together
Every one should stay in the same room or be on the same path and not stray away from each other. There are times that you need to buy more ammo or get a new gun in this case you should go split into teams of two but if you are a group of three or two you need to decide what to. When the group stays together it becomes easier to move around the map during a middle of a wave and you save ammo because teammates are also shooting the zombies saving you some ammo.
5. When not to revive
There is going to be a time when you face the choice to save a teammate or run. Know what to do can effect how far you go because if you run there might be time to kill the mob be hind you and save them but they might die making you start the next round on the weak side. Every time this happens it is going to different what gun / perks you have were they went down and how far away the zombies are. If zombies are half way down a hallway and you have quick revive a revive is possible but might be a closes call and 100% of the time it is a judgment you have to make.
6. keeping crawlers
A very common problem is not having a crawler at the end of round to resupply for the next round. Crawlers should be created when you are close to the end of a wave and you are low on ammo, can upgrade a gun or need perks. It is important that every in the group knows how many crawlers and tell others if they kill one because if two people need points and there are only two crawlers they can only get the points from the crawlers they will each kill a crawler and start the next round by accident. Another common accident is some one makes some crawlers early and the players fighting the mob will shoot them. When making crawlers make sure it is close to the end of the wave or keep a zombie at a window.
What to remember? Make sure you guns can kill a zombie with as few bullets as possible ,Watch your ammo supply, have a good camp area, manage your points, Stay together, some times it is better to run then to revive, and have a crawler when you need it.